Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare idempotentHint=true, openWorldHint=true, readOnlyHint=false and destructiveHint=false, so the safety profile is covered. The description still adds real context beyond structured fields: the account must be on the Vault plan, and it restates idempotency in observable terms ('adding the same watch twice changes nothing'). It does not say what error or result appears when the plan requirement is unmet.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Three short sentences, front-loaded with the action and resource, then the input convention, then the idempotency note. No filler and nothing that belongs only in a schema.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a two-parameter mutation tool with no output schema, annotations cover safety and the description covers the plan prerequisite, input format, and idempotency. The remaining gap is what happens on failure (non-Vault account, unrecognized link) and whether the added watch is immediately active in Radar, but nothing essential to correct invocation is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is only 50%: the 'kind' enum (artist/track) is self-documenting, and the 'text' format is already spelled out in its schema description, so the description's 'For a track, send "Artist - Title" or a store link' largely repeats structured data. It adds a 500-char-bounded free-text expectation but nothing about how the store-link form is parsed, so it does not compensate for the modest coverage gap.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description gives a specific verb ('Add') plus resource ('artist or track to this account's Radar') and a cardinality constraint ('one'), which cleanly separates it from siblings such as remove_radar_watch and get_radar. An agent knows exactly what state change this produces without opening the schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

It states the prerequisite (Vault plan) and the input convention for a track watch ('Artist - Title' or a store link), which tells the agent when this call is applicable. It does not name remove_radar_watch or get_radar as the natural alternatives for the opposite operations, so the routing guidance is implicit rather than explicit.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.